Three-electron gun assembly with electrically connecting and supporting plate for the control grids



Feb. 6, 1968 D. LEVIN 3,368,097

N. THREE-ELECTRON GUN ASSEMBLY WITH ELECTRICALLY CONNECTING AND SUPPORTING PLATE FOR THE CONTROL GRIDS Filed Sept. 6, 1966 IN V EN TOR. Nat/2am D. Lew/z 16 %,a, a mfi United States Patent Ofiice THREE-ELECTRON GUN ASSEMBLY WITH ELEC- TRICALLY CONNECTING AND SUPPORTING PLATE FOR THE CONTROL GRIDS Nathan D. Levin, Highland Park, Ill., assignor to Admiral Corporation, Chicago, 11]., a corporation of Delaware Filed Sept. 6, 1966, Ser. No. 577,390 3 Claims. (Cl. 31382) This invention relates in general to electron gun as- .semblies and in particular to tri-gun assemblies for color television picture tubes.

The trigun assembly, which is in widespread use in commercial color television picture tubes, employs three individual electron gun structures to produce three separate electron beams. These individual gun structures, comprising a number of cupshaped elements or grids positioned along a common axis, are arranged symmetrically around a center axis. The gun elements are held in their proper positions by bars of rigid, nonconductive material, such as glass or ceramic (multiform), in which support tabs attached to the individual elements are embedded.

It is well known that the focus control grids, commonly called the G 3 grids, are operated at the same potential. Consequently, an internal interconnection means is commonly employed for this purpose. Since the G-3 grids operate to focus the electron beams, it is also desirable to maintain a rigid mechanical alignment of these grids; and a support plate which accomplishes both the electrical interconnection'and rigid alignment is often used. This support plate is placed transverse to the center axis of the tri-gun arrangement, and in the past the center section of this support plate has generally comprised a mass of material mutually interconnecting the three G-3 grids.

It is also well known to subject the electron gun assembly to radio frequency (RF) bombardment after it has been scaled into the neck of the picture tube. This operation takes place during the exhausting of the tube and is accomplished by way of a coil placed around the neck of the tube. The R.F. bombardment results in induction heating of the elements in the gun assembly which drives off gas therefrom so that subsequent in use heating will not drive off further gas. However, because of its particular position in the electron gun assembly, the support plate is transverse to the axis of the RF. coil and is thus highly responsive to the RF. field. Moreover, since the plate mutually interconnects the three grids, it acts as a shorted turn in the RF. field. As a result, a current of large magnitude is induced in the plate and the plate becomes extremely hot, sometimes as much as 100 hotter than the other elements in the assembly. This extreme heating of the support plate has at least two undesirable effects: the supoprt plate absorbs an unwarranted amount of energy from the RP. field, which energy is consequently not available to heat the other elements, and the welds which attach the support plate to the G-3 grids are subjected to great stress due to differential expansion, often resulting in the breaking of these welds and a malfunctioning of the electron gun assembly. This malfunctioning results in a defective finished tube.

Therefore, it is the primary object of this invention to provide an improved electron gun assembly for a trigun color television picture tube.

It is a further object of this invention to provide a tri-gun assembly in which the support plate for the G-3 grids does not act as a shorted turn during R.F. bombardment.

3,368,097 Patented Feb. 6, 1968 This invention features a tri-gun assembly in which the support plate for the G3 grids does. not mutually interconnect the three grids, but rather has a discontinuity between a pair of the grids to prevent the plate acting as a shorted turn during R.F. bombardment. The advantages of this support plate are apparent. Since it does not act as a shorted turn, there is no current of large magnitude induced in the plate, and consequently the plate is not heated to any significantly greater degree than the rest of the gun assembly. The welds attaching the plate to the grids are not subjected to stress so the number of defective tubes due to malfunctioning gun assemblies is reduced.

Other objects, features, and advantages of this invention will be apparent from a reading of the following specification in conjunction with the accompanying drawing in which:

FIG. 1 is an elevation view of a tri-gun assembly for a color television picture tube.

FIG. 2 is a section view taken along the line 2-2 in FIG. 1 which shows the G-3 support plate of this invention.

In FIG. 1 an electron gun assembly 10 comprising three separate electron gun structures arranged in a delta fashion around a center axis is shown. In practice, this electron gun assembly is mounted in the neck of a picture tube (not shown) and connections are made to the gun elements through the base (not shown) of thetube.

Each of the individual electron gun structures comprises a number of cup-shaped elements or grids having different sized apertures therethrough and being arranged along a common axis. Voltages of appropriate magnitude are applied to the gun elements and to the heater and cathode (not shown) to produce a beam of electrons moving at a high velocity. The details of operation are well known and need not be discussed here.

The foremost electron gun structure of tri-gun assembly 10 includes a control (G-l) grid 14, an accelerating (G2) grid 15, a focus control (G-3) grid 16, and a second accelerating (6-4) grid 17. The cathode and heater assemblies (not shown) are nested in control grid 14. Each of the grids, 14, 15, 16, and 17, has a support tab 19 attached to it, and the support tabs are embedded in glass multiform 11 to hold the grids in position. G-4 grid 17 is attached to a convergence assembly 18 which is common to all three gun structures. Snubber springs 13 serve to connect convergence assembly 18 to the conductive coating on the inside of the picture tube (not shown) and also help to center and support gun assembly 10 within the tube neck. A support plate 20 is attached to G-S grid 16 and to the G-3 grids of the other two electron gun structures in the assembly. As will be seen more clearly in FIG. 2, this support plate 20 provides a rigid mechanical alignment of the G-3 grids and at the same time interconnects them electrically.

In FIG. 2 the details of support plate are shown. Center section 21 of support plate 25 is generally triangular shaped, and from each side of center section 21 a pair of arms 22 extend. Each pair of arms 22 embraces one of the G-3 grids 16, and each arm 22 is tack welded at points 26 to a flat portion 24 on its associated G-3 grid. Support plate 20 is precisely sized, and its physical attachment to the G-3 grids 16 provides a rigid mechanical alignment of these grids. Moreover, support plate 20 is made from a material which is a good conductor of electricity so it provides an electrical interconnection of the three G-3 grids 16 as well. External connection to one of the interconnected G-3 grids can be made by means of a strap 27.

Center section 21 is shown with an aperture 28 therethrough and a slit 25 which extends from aperture 2810 one of the apices of center section 21. Aperture 28, which may be used for gun aligning purposes, and slit 25 create a discontinuity in support plate 20 between the G-3 grids on either side of the slit. As a result of this discontinuity, support plate 20 does not mutually interconnect all three G-3 grids 16. The importance of this absence of mutual interconnection becomes apparent when it is considered that electron gun assembly is subjected to RF. bombardment after being sealed into the picture tube neck (not shown). The RF. bombardment is accomplished by means of a coil (not shown) placed around the neck of the tube so that the axis of the electron gun assembly is parallel to the axis of the coil. Since support plate 26 is in a position transverse to the axes of the gun assembly and coil, it is highly responsive to the RF. field. If the discontinuity created by aperture 28 and slit 25 were not present, support plate 20 would act as a shorted turn, and the high current induced in the plate would heat it to a temperature much higher than the other elements in the gun assembly. Also, the support plate would absorb an unwarranted amount of energy from the RF. field and thereby lower the temperatures of the other gun elements.

If support plate 20 were heated to a temperature much higher than the G-3 grids 16, differential expansion of the plate and the grids would place a great amount of stress on the welds which attach them together, and some of the welds would break. Breaking of the welds would result in electrical malfunctioning of the G-3 grids, and the electron gun assembly would be defective. Moreover, a detective electron gun assembly would lead to a rejected picture, tube. However, by providing the electrical discontinuity in support plate 20 between a pair of 6-3 grids, the support plate is precluded from acting as a shorted turn, and there is no excessive heating of the plate. The problem of breaking of welds is eliminated by this invention, and thus the reject rate of finished picture tubes due to malfunctioning gun assemblies is reduced.

While the above description is made with reference to a preferred embodiment of this invention, it is apparent that numerous modifications could be made without departing from the scope of this invention as claimed in the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electron gun assembly for a color television picture tube, said assembly adapted to be subjected to RP. bombardment during the processing of said tube, comprising three similar electron gun structures arranged symmetrically around a center axis for producing three separate electron beams, each of said gun structures including a plurality of substantially cup-shaped elements; means supporting said elements in a substantially fixed relationship; and structural means providing rigid mechanical alignment and coincident electrical interconnection of a particular set of corresponding elements, said electrical interconnection being discontinuous between a pair of said corresponding elements to preclude said structural means acting as a shorted turn during said R.F. bombardment.

2. An electron gun assembly as claimed in claim 1, wherein said structural means is a plate arranged transverse to said center axis and attached to each of said elements in said particular set, said plate having a discontinuity between a single pair of said elements so that said elements of said single pair are electrically connected only by way of the portion of said plate attached to the remaining element in said particular set.

3. An electron gun assembly as claimed in claim 2, wherein said plate has a generally triangular center section with a pair or arms extending from each side of said center section and embracing one of said elements in said particular set, each of said arms being welded to its corresponding element, said center section having an aperture therein which may be used for gun aligning purposes and a slit extending from said aperture to one of the apices of said center section, said aperture and said slit creating a discontinuity in said plate between the elements on either side of said slot.

References Cited UNITED STATES PATENTS 3,011,090 11/1961 Moodey 313- X 3,268,753 8/1966 Hughes 313-70 X 3,324,328 6/1967 Burdick et al. 313-70 X DAVID J. GALVIN, Primary Examiner.

V. LAFRANCHI, Assistant Examiner. 

1. AN ELECTRON GUN ASSEMBLY FOR A COLOR TELEVISION PICTURE TUBE, SAID ASSEMBLY ADAPTED TO BE SUBJECTED TO R.F. BOMBARDMENT DURING THE PROCESSING OF SAID TUBE, COMPRISING THREE SIMILAR ELECTRON GUN STRUCTURES ARRANGED SYMMETRICALLY AROUND A CENTER AXIS FOR PRODUCING THREE SEPARATE ELECTRON BEAMS, EACH OF SAID GUN STRUCTURES INCLUDING A PLURALITY OF SUBSTANTIALLY CUP-SHAPED ELEMENTS; MEANS SUPPORTING SAID ELEMENTS IN A SUBSTANTIALLY FIXED RELATIONSHIP; AND STRUCTURAL MEANS PROVIDING RIGID MECHANICAL ALIGNMENT AND COINCIDENT ELECTRICAL INTERCONNECTION OF A PARTICULAR SET OF CORRESPONDING ELEMENTS, SAID ELECTRICAL INTERCONNECTION BEING DISCONTINUOUS BETWEEN A PAIR OF SAID CORRESPONDING ELEMENTS TO PRECLUDE SAID STRUCTURAL MEANS ACTING AS A SHORTED TURN DURING SAID R.F. BOMBARDMENT. 